1. Field of the Invention
The present invention relates to a device and a method for measuring a thickness and a weight per unit area of a microporous film formed on an electrode plate for a battery, as well as a coater equipped with the film measuring device, and a coating method using the film measuring method.
2. Description of the Related Art
Heretofore, there has been used a technique of measuring the weight per unit area of a microporous film formed on an electrode plate for a battery, as disclosed in Japanese Laid-Open Patent Publication No. H8 (1996)-96806 (D1), for instance. In D1, a β-ray emitter and a detector are arranged as opposed to each other, with an electrode material being fed in a certain direction between the β-ray emitter and the detector. The β-ray emitter and the detector are moved in cooperation with each other in a width direction of a film to be measured, i.e. in a direction orthogonal to the feeding direction of the electrode material. During the movements of the β-ray emitter and the detector, the β-ray emitter emits β-rays, and the detector detects the amount of the β-rays transmitted through the electrode material. The weight per unit area of the microporous film is measured by comparing a detection result on the β-ray transmission with a reference transmission amount.
In the above arrangement, the measurement sites are only the positions where the β-ray emitter and the detector are moved, and accordingly, it is impossible to conduct the measurement for the entire area of the electrode material. Also, it is hazardous to handle β-rays. The installation condition for the β-ray emitter is constrained because a radioactive ray is used. Further, a qualified staff is required to operate the β-ray emitter, which hinders usability of the β-ray emitter. In addition, the β-ray emitter is expensive. Furthermore, since the microporous film is thin, a variation in β-ray transmission amount due to a thickness variation of the microporous film is significantly small. Also, the variation in β-ray transmission amount is smaller than a variation in β-ray transmission amount due to thickness variations of a metal sheet as a base member, and an active material layer, which makes the weight detection difficult. Further, even if a fluorescent X-ray is used in place of the β-ray, a variation in fluorescent X-ray transmission amount is significantly small, and an attenuation of the fluorescent X-ray in the air is significantly large, which also makes the weight detection difficult.
Japanese Laid-Open Patent Publication No. H8 (1996)-309262 (D2) proposes a film thickness measuring device constructed such that: a UV ray is irradiated onto a surface of a golf ball coated with a clear coat made of a clear coating material containing a fluorescent brightening agent; secondary emission rays obtained by the UV ray irradiation are captured by a CCD camera; a contrast image is obtained by multilevel-processing the acquired image data; and the thickness of the coat is measured based on the contrast image.
It is, however, impossible to measure the film thickness, unless the film has a property responsive to a specific wavelength, even by modifying the art recited in D2 so as to measure the thickness of the film formed on the film-like or sheet-like base member.